.\" -*- nroff -*-
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2007-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Win_start 3 "Jun 10, 2020" "4.0.4" "Open MPI"
.SH NAME
\fBMPI_Win_start\fP \- Starts an RMA access epoch for \fIwin\fP

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Win_start(MPI_Group \fIgroup\fP, int assert, MPI_Win \fIwin\fP)

.fi
.SH INPUT PARAMETERS
.ft R
.TP 1i
group
The group of target processes (handle).
.TP 1i
assert
Program assertion (integer).
.TP 1i
win
Window object (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
MPI_Win_start is a one-sided MPI communication synchronization call that starts an RMA access epoch for \fIwin\fP. RMA calls issued on \fIwin\fP during this epoch must
access only windows at processes in \fIgroup\fP. Each process in \fIgroup\fP must issue a matching
call to MPI_Win_post. MPI_Win_start
is allowed to block until the corresponding MPI_Win_post calls have been executed, but is not required to.
.sp
The \fIassert\fP argument is used to provide assertions on the context of the call that may be used for various optimizations. (See Section 6.4.4 of the MPI-2 Standard.) A value of \fIassert\fP = 0 is always valid. The following assertion value is supported:
.sp
.TP 1i
MPI_MODE_NOCHECK
When this value is passed in to this call, the library assumes that
the post call on the target has been called and it is not necessary
for the library to check to see if such a call has been made.

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.
.sp
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Win_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

.SH SEE ALSO
MPI_Win_post
MPI_Win_complete
.br

